dm: add unstriped target

This device mapper "unstriped" target remaps and unstripes I/O so it
is issued solely on a single drive in a HW RAID0 or dm-striped target.

In a 4 drive HW RAID0 the striped target exposes 1/4th of the LBA range
as a virtual drive.  Each I/O to that virtual drive will only be issued
to the 1 drive that was selected of the 4 drives in the HW RAID0.

This unstriped target is most useful for Intel NVMe drives that have
multiple cores but that do not have firmware control to pin separate LBA
ranges to each discrete cpu core.

Signed-off-by: Scott Bauer <scott.bauer@intel.com>
Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Acked-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 225 insertions, 0 deletions

diff --git a/drivers/md/dm-unstripe.c b/drivers/md/dm-unstripe.c
new file mode 100644
index 000000000000..061b4f10bf5c
--- /dev/null
+++ b/drivers/md/dm-unstripe.c
@@ -0,0 +1,225 @@
+/*
+ * Copyright (C) 2017 Intel Corporation.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm.h"
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+#include <linux/bitops.h>
+#include <linux/device-mapper.h>
+
+struct unstripe_c {
+	struct dm_dev *dev;
+	sector_t physical_start;
+
+	uint32_t stripes;
+
+	uint32_t unstripe;
+	sector_t unstripe_width;
+	sector_t unstripe_offset;
+
+	uint32_t chunk_size;
+	u8 chunk_shift;
+};
+
+#define DM_MSG_PREFIX "unstriped"
+
+static void cleanup_unstripe(struct unstripe_c *uc, struct dm_target *ti)
+{
+	if (uc->dev)
+		dm_put_device(ti, uc->dev);
+	kfree(uc);
+}
+
+/*
+ * Contruct an unstriped mapping.
+ * <number of stripes> <chunk size> <stripe #> <dev_path> <offset>
+ */
+static int unstripe_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+	struct unstripe_c *uc;
+	sector_t width, tmp_len;
+	unsigned long long start;
+	char dummy;
+
+	if (argc != 5) {
+		ti->error = "Invalid number of arguments";
+		return -EINVAL;
+	}
+
+	uc = kzalloc(sizeof(*uc), GFP_KERNEL);
+	if (!uc) {
+		ti->error = "Memory allocation for unstriped context failed";
+		return -ENOMEM;
+	}
+
+	if (kstrtouint(argv[0], 10, &uc->stripes) || !uc->stripes) {
+		ti->error = "Invalid stripe count";
+		goto err;
+	}
+
+	if (kstrtouint(argv[1], 10, &uc->chunk_size) || !uc->chunk_size) {
+		ti->error = "Invalid chunk_size";
+		goto err;
+	}
+
+	// FIXME: must support non power of 2 chunk_size, dm-stripe.c does
+	if (!is_power_of_2(uc->chunk_size)) {
+		ti->error = "Non power of 2 chunk_size is not supported yet";
+		goto err;
+	}
+
+	if (kstrtouint(argv[2], 10, &uc->unstripe)) {
+		ti->error = "Invalid stripe number";
+		goto err;
+	}
+
+	if (uc->unstripe > uc->stripes && uc->stripes > 1) {
+		ti->error = "Please provide stripe between [0, # of stripes]";
+		goto err;
+	}
+
+	if (dm_get_device(ti, argv[3], dm_table_get_mode(ti->table), &uc->dev)) {
+		ti->error = "Couldn't get striped device";
+		goto err;
+	}
+
+	if (sscanf(argv[4], "%llu%c", &start, &dummy) != 1) {
+		ti->error = "Invalid striped device offset";
+		goto err;
+	}
+	uc->physical_start = start;
+
+	uc->unstripe_offset = uc->unstripe * uc->chunk_size;
+	uc->unstripe_width = (uc->stripes - 1) * uc->chunk_size;
+	uc->chunk_shift = fls(uc->chunk_size) - 1;
+
+	width = ti->len;
+	if (sector_div(width, uc->stripes)) {
+		ti->error = "Target length not divisible by number of stripes";
+		goto err;
+	}
+
+	tmp_len = width;
+	if (sector_div(tmp_len, uc->chunk_size)) {
+		ti->error = "Target length not divisible by chunk size";
+		goto err;
+	}
+
+	if (dm_set_target_max_io_len(ti, uc->chunk_size)) {
+		ti->error = "Failed to set max io len";
+		goto err;
+	}
+
+	ti->private = uc;
+	return 0;
+err:
+	cleanup_unstripe(uc, ti);
+	return -EINVAL;
+}
+
+static void unstripe_dtr(struct dm_target *ti)
+{
+	struct unstripe_c *uc = ti->private;
+
+	cleanup_unstripe(uc, ti);
+}
+
+static sector_t map_to_core(struct dm_target *ti, struct bio *bio)
+{
+	struct unstripe_c *uc = ti->private;
+	sector_t sector = bio->bi_iter.bi_sector;
+
+	/* Shift us up to the right "row" on the stripe */
+	sector += uc->unstripe_width * (sector >> uc->chunk_shift);
+
+	/* Account for what stripe we're operating on */
+	sector += uc->unstripe_offset;
+
+	return sector;
+}
+
+static int unstripe_map(struct dm_target *ti, struct bio *bio)
+{
+	struct unstripe_c *uc = ti->private;
+
+	bio_set_dev(bio, uc->dev->bdev);
+	bio->bi_iter.bi_sector = map_to_core(ti, bio) + uc->physical_start;
+
+	return DM_MAPIO_REMAPPED;
+}
+
+static void unstripe_status(struct dm_target *ti, status_type_t type,
+			    unsigned int status_flags, char *result, unsigned int maxlen)
+{
+	struct unstripe_c *uc = ti->private;
+	unsigned int sz = 0;
+
+	switch (type) {
+	case STATUSTYPE_INFO:
+		break;
+
+	case STATUSTYPE_TABLE:
+		DMEMIT("%d %llu %d %s %llu",
+		       uc->stripes, (unsigned long long)uc->chunk_size, uc->unstripe,
+		       uc->dev->name, (unsigned long long)uc->physical_start);
+		break;
+	}
+}
+
+static int unstripe_iterate_devices(struct dm_target *ti,
+				    iterate_devices_callout_fn fn, void *data)
+{
+	struct unstripe_c *uc = ti->private;
+
+	return fn(ti, uc->dev, uc->physical_start, ti->len, data);
+}
+
+static void unstripe_io_hints(struct dm_target *ti,
+			       struct queue_limits *limits)
+{
+	struct unstripe_c *uc = ti->private;
+
+	limits->chunk_sectors = uc->chunk_size;
+}
+
+static struct target_type unstripe_target = {
+	.name = "unstriped",
+	.version = {1, 0, 0},
+	.module = THIS_MODULE,
+	.ctr = unstripe_ctr,
+	.dtr = unstripe_dtr,
+	.map = unstripe_map,
+	.status = unstripe_status,
+	.iterate_devices = unstripe_iterate_devices,
+	.io_hints = unstripe_io_hints,
+};
+
+static int __init dm_unstripe_init(void)
+{
+	int r;
+
+	r = dm_register_target(&unstripe_target);
+	if (r < 0)
+		DMERR("target registration failed");
+
+	return r;
+}
+
+static void __exit dm_unstripe_exit(void)
+{
+	dm_unregister_target(&unstripe_target);
+}
+
+module_init(dm_unstripe_init);
+module_exit(dm_unstripe_exit);
+
+MODULE_DESCRIPTION(DM_NAME " unstriped target");
+MODULE_AUTHOR("Scott Bauer <scott.bauer@intel.com>");
+MODULE_LICENSE("GPL");